3.2 Performance Considerations
CSS performance affects both initial page load times and runtime performance. We minify and compress all CSS for production, but the way we write CSS also impacts performance. Avoiding deeply nested selectors and overly specific rules helps the browser parse and apply styles more efficiently.
We leverage CSS custom properties (variables) for consistent theming and easier maintenance, but we’re mindful of their performance implications in older browsers. Critical above-the-fold CSS can be inlined in the document head to eliminate render-blocking requests, while non-critical styles are loaded asynchronously.
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// Using CSS custom properties for consistent theming
:root {
--color-primary: #2563eb;
--color-primary-dark: #1d4ed8;
--color-secondary: #059669;
--font-family-base: system-ui, -apple-system, sans-serif;
--font-size-base: 1rem;
--line-height-base: 1.6;
--spacing-unit: 1rem;
}
// Component using the custom properties
.card {
background: white;
border-radius: calc(var(--spacing-unit) * 0.5);
padding: var(--spacing-unit);
font-family: var(--font-family-base);
line-height: var(--line-height-base);
}